Clinical Overview of Heat and Pregnancy

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Key points

  • Heat can harm a pregnant woman's health during any trimester. Remind pregnant women to check the HeatRisk forecast every day during warm months and take protective action when HeatRisk is orange or higher.
  • There are several ways to stay healthy when it's hot outside. Create a Heat Action Plan with your pregnant patients.
  • Exposure to heat can lead to health harms for pregnant women, to pregnancy complications, and to adverse pregnancy outcomes. As little as one day of high heat may increase risk.
  • Encourage your pregnant patients to check the air quality index (AQI) daily and take protective action when the AQI is >100, since hot days can also worsen air quality. Breathing polluted air can harm pregnant women.
  • Review commonly prescribed medications with your pregnant patients, such as antihistamines or antihypertensive medications, since they may increase heat sensitivity. Periodic review of medications before and during the heat season may prevent harm.
Pregnancy

Background

This guidance document is intended to help support your conversations with pregnant women on the impact of heat on pregnancy. The information provided can empower them to take protective actions on hot days. While not everyone may be able to take all actions, each action can help a pregnant women stay healthy during hot days.

Pregnancy and heat exposure

Being outside can provide many health benefits. Exposure to heat, however, can lead to health harms for pregnant women and pregnancy complications, including from hypertensive disorders of pregnancy. Heat can place added stress on the heart and cardiovascular system which is already undergoing normal physiologic changes during pregnancy, including increased blood volume, cardiovascular output, and heart rate.

Heat exposure in any trimester has been associated with adverse pregnancy outcomes including preterm births, stillbirths, and low birthweight infants. In addition, heat exposure during the first trimester of pregnancy may increase the risk of certain birth defects.

Risk for adverse pregnancy outcomes increases with increasing temperatures and longer heat exposure, although as little as one day of high heat, defined as above the 95th percentile of mean temperature, may increase risk.

Heat, air quality, and pregnancy

Hot days can promote unhealthy levels of air pollutants, including ozone, fine particulate matter, and sulfur dioxide. Breathing polluted air causes inflammation and epigenetic changes that can interfere with placental blood flow and development, as well as promote blood clot formation. Exposure to both heat and air pollution together can increase the risk of adverse pregnancy outcomes, including preterm births, compared to either weather event alone.

Hot and dry weather can also increase the risk of wildfires. Wildfire smoke pollutants are known to be associated with adverse birth outcomes.

Breathing polluted air can be particularly unsafe for pregnant women with asthma. Asthma can contribute to pregnancy complications and adverse pregnancy outcomes such as preterm birth, low birth weight infants, and perinatal mortality, with a higher likelihood for these events for pregnant women with asthma who are exposed to poor air quality. Pregnant women with asthma may benefit from including steps to reduce heat and poor air quality exposure in both their Heat Action Plan and their Asthma Action Plans.

Pregnant women working in hot environments may be able to request reasonable accommodations in the workplace to reduce heat stress, such as increased breaks to cool down, hydrate, and use a bathroom.

Risk factors

Heat, medications, and pregnancy

Medications and heat can interact, leading to potentially severe side effects. Many medications taken during pregnancy, including over the counter medications and those used to treat high blood pressure, can impair heat tolerance and the body's ability to regulate its temperature. This can predispose people to heat illness during hot days which can lead to pregnancy complications.

Medications should be carefully reviewed with attention to those that may affect heat tolerance or fluid balance. Review any necessary changes to medications on hot days with your pregnant patients and work with your patient to document them in their Heat Action Plan.

Learn more about how heat and medications can interact

Review the Heat and Medications page for important information on how heat and medications interact, which medications are commonly impacted by heat, and how to approach a medication and heat action plan with your patients.
Heat and Medications – Guidance for Clinicians

Patient management

These 5 steps can help your pregnant patients stay safe on hot days. Help your patients document action steps in a Heat Action Plan.

  1. Assess heat- and air quality-related risk factors that may lead to pregnancy complications.
    • Review your patient’s underlying health status and determine if any co-existing health conditions may increase the risk of heat harms during pregnancy, including asthma or hypertension. If a pregnant woman has these conditions and they are not well controlled, she may be more sensitive to heat and poor air quality and may be more likely to have pregnancy complications.
    • Use the HEAT questionnaire to assess risk factors related to
      • Housing and Indoor Environment
      • Emergency Preparedness
      • Awareness of Health Risks
      • Temperature and Outdoor Environment
    • Based on risk factor screening, refer your patient to needed services or engage social work support in your clinic as appropriate.
  1. Educate your patients on how to stay cool during hot days.
    • Review the HeatRisk Tool and how it works with your patients. The tool assigns colors to each level of risk and recommends protective actions by color level.
      • Ask your patients to monitor their symptoms at HeatRisk yellow and orange and determine which level applies to them. Their Heat Action Plan should reflect the applicable HeatRisk level.
      • Most patients can take action when the HeatRisk is orange.
      • Some people will be more sensitive to heat and will need to take action when HeatRisk is yellow.
    • In addition to the recommended actions to take when outside for each level of HeatRisk, everyone can
      • Wear light-colored, loose-fitting clothing that covers arms and legs, a hat with a brim that shades the face, ears, and back of the neck, and sunglasses.
      • Apply broad spectrum sunscreen that filters out UVA and UVB rays. The sunscreen should have an SPF of 30 or higher.
      • Schedule outdoor activities during the coolest time of the day or evening, if possible.
    • Review heat-related symptoms with your patients.
      • Review the signs of heat-related illness and pregnancy warning signs with your patients. Symptoms of heat-related illness include heavy sweating, muscle cramps, weakness, lightheadedness, headache, nausea, vomiting and preterm contractions.
      • Help them understand signs and symptoms that their underlying health conditions may be worsened by heat (for example, worse blood sugar control in pregnant patients with diabetes).
      • Help your patients understand the difference between heat exhaustion and heat stroke.
      • Review which symptoms constitute an emergency and what actions to take in an emergency setting.
    • Talk to your patients about how to stay cool indoors. They can
      • Use an air conditioner if they have one or find a location that does. Even a few hours in a cool location can lower the health risk from heat.
      • Use fans if indoor temperatures are less than 90°F. In temperatures above 90°F, a fan can increase body temperature.
      • Cool their bodies with a cool shower, a damp cool cloth, or a spray bottle of cool water.
    • Direct your patients to information about public resources such as cooling centers, pools, and splash pads. The nearest cooling center locations can be located by calling 2-1-1, checking public resources, or contacting your local health department and/or emergency management agency.
    • Refer patients who need assistance with home energy costs to the Low-Income Heat Energy Assistance Program (LIHEAP).
  1. Educate your patient on how to stay hydrated.
    • Review signs and symptoms of dehydration, which include

    Cold, clammy skin
    Dizziness or feeling lightheaded
    Rapid heart rate
    Excessive sweating or an inability to sweat
    Fatigue
    Headache
    Muscle cramps or spasms

    Nausea
    Abdominal cramping
    Swelling in extremities
    Darker color urine
    Infrequent urination
    Thirst
    Preterm contractions

    • Emphasize the importance of regular and consistent fluid and food intake throughout the day.
    • Advise patients to try to limit beverages higher in sugars, sodium, and caffeine, which may lead to dehydration. See Guideline 4 of the dietary guidelines.
    • Advise patients that water is usually the best choice, although sports drinks containing electrolytes may be necessary if sweating for several hours.
    • Remind patients that alcohol can cause dehydration and may worsen the risk of heat related illness if consumed when in hot settings.
    • Since pregnant patients may restrict sodium intake, remind them to look at the sodium content of beverages.
    • Remind pregnant patients to monitor for signs and symptoms of fluid overload and dehydration on hot days. Consider fluids with electrolyte supplements as needed.
    • Pregnant women with nausea, vomiting, and diarrhea will need particular attention to avoiding dehydration and fluid and electrolyte imbalance, which heat exposure can compound.
    • To avoid sunburn, which can promote dehydration, see # 2 above, “How to Stay Cool”.
  1. Educate your patients on air quality. Heat can worsen air quality, which can lead to additional health harms.

Did you know?

About the Air Quality Index and Actions to Consider at Each Level

The AQI reports air quality for common air pollutants such as ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Its value ranges from 1 to 500, with higher numbers corresponding to worse air quality and greater health concerns.

When the number is above 100, outdoor air is considered unhealthy for sensitive groups including pregnant women.On days with an AQI > 100, it is okay to be outside, but it may be helpful to take more breaks and do less intense activities. If they have asthma, they can follow their asthma action plan and keep quick relief medicine handy.

Some pregnant women may be sensitive to air pollution at lower AQI levels, when the AQI is between 51 and 100. Ask your patients to use the AQI to assess whether they are sensitive to the air quality when the AQI is between 51 and 100 or only at an AQI >100. Based on this, refer them to actions to take at AQI levels that lead to breathing sensitivity for them and ask that they include this in their heat action plans.

It is important to be aware that the Air Quality Index does not include pollen counts. This means that on some days, the Air Quality Index may be low even though pollen levels in the air are high.

  1. Make a plan with your patients for medication management on HeatRisk orange, red, and magenta days.
    • Review the Heat and Medications page to familiarize yourself with how medications interact with heat, which medications are most likely to do so, and an approach to medication management during hot days.
    • Ensure your pregnant patients know to not abruptly stop medications and to take all medications as directed unless otherwise guided by you or another clinician.
    • Review your patient’s medication list with them, highlighting medications that may need to be adjusted because of interactions with heat, including antihypertensive agents or diuretics. Document with your patient any medication adjustments during hotter weather and when to resume their normal medication schedule.
    • For a pregnant woman with asthma, review the Asthma Action Plan and consider any necessary changes to asthma medications on hot days.
    • Provide guidance on proper storage of medications, including for medications that individuals may carry with them, such as inhalers, which can malfunction or burst from high heat. Counsel patients not to leave medications in places that can get excessively hot and help your patients develop a power outage plan for medications requiring refrigeration like insulin and for electric medical devices like nebulizer machines, ventilators, and oxygen concentrators in the event of a heat-related power outage.
    • Counsel your patients to limit sun exposure if they take a medication that can cause sensitivity to the sun, such as certain antibiotics.
    • Encourage your patients to reflect heat and medication information discussed with you in the medication section of their Health Action Plan.
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Content Source:
National Center for Environmental Health (NCEH)